Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with agraphical user interface showing my new design, the graphical userinterface shown separately for ease of illustration; and,

FIG. 2 is a front view thereof, shown with environment.

The broken line showings of the text, numbers, and images in FIGS. 1 and2 and the mobile device in FIG. 2 are included for the purpose ofillustrating portions of the article and form no part of the claimeddesign.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.